This invention relates to electro-optical devices and more particularly to devices whose electromagnetic radiation transmission characteristics can be selectively altered by the influence of a suitably controlled electric field. Still more particularly the invention is concerned with an electro-optical device in which a liquid electrolyte is employed in a cell containing an electrochromic material of variable oxidation states, such as tungsten oxide of titanium dioxide.
In prior U.S. applications, Ser. No. 530,086, filed Feb. 25, 1966 and Ser. No. 534,188, filed Mar. 14, 1966 and continuation-in-part applications thereof, there are described electro-optical devices exhibiting a phenomenon known as persistent electrochromism. This term denotes the property of a material whereby its electromagnetic radiation absorption characteristic is altered, in most instances even at ambient temperature, under the influence of an electric field. Such materials, for example, may exhibit little or no absorption of visible wave lengths in the absence of an electric field and therefore be transparent, but when subjected to an electric field, effectively absorb in the red end of the spectrum, turning blue in color. Similar effects can be observed in other portions of the electromagnetic radiation spectrum, invisible as well as visible.
As described in the foregoing earlier applications, if an assembly is formed wherein a layer of a persistent electrochromic material is disposed between a pair of electrodes, across which a potential is applied, the radiation transmitting characteristic of the material will change. If the electrodes and the electrochromic layer are formed on the surface of a transparent substrate, such as glass, the light transmitting characteristics of the combination can be varied by controlling the electric field produced across the electrochromic layer. Thus, if the "sandwich" of electrodes and electrochromic material on the substrate originally is clear, i.e., presenting substantially no diminution of the light transmitting ability of the substrate, application of a voltage between the electrodes to establish an electric field of the proper polarity changes the light absorption characteristic of the electrochromic material, turning it darker, for example, thus decreasing the light transmitting ability of the entire assembly.